Flip chip in leaded molded package and method of manufacture thereof

ABSTRACT

A chip device that includes a leadframe, a die and a mold compound. The backside of the die is metallized and exposed through a window defined within a mold compound that encapsulates the die when it is coupled to the leadframe. Leads on the leadframe are coupled to source and gate terminals on the die while the metallized backside of the die serves as the drain terminals.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an improved package and methodof packaging for a flip chip, and more particularly, to a flip chipwherein a die is attached to a leadframe that is then placed within athinner package such that the back side of the die is exposed.

[0003] 2. Description of the Prior Art

[0004] In power transistor packages, those in the art are generallystill using chip and wire bond interconnect technology. It is difficultto simplify the manufacturing process flow as all process steps, suchas, for example, die attach, wire bond, and molding are required. As aresult, there is a limit placed on the maximum size for the die. Thus,power transistor packages are suited for single die applications sinceformation of an isolated metal pad for power transistor packages thatinclude multiple dies is very difficult.

[0005] Recent attempts to improve packaging of chip devices haveincluded directly coupling lead frames to the die. However, thistechnology does not lend itself well to the manufacture of thinneroutline (or profile) packages. Hence, such packages, as well as thoseusing wire bond interconnect technology, tend to be thick.

SUMMARY OF THE INVENTION

[0006] The present invention provides a chip device that includes aleadframe including a plurality of leads and a die coupled to theleadframe. The die includes a metallized back side as well as source andgate terminals opposite the metallized backside. The die is coupled tothe leadframe such that the leads of the leadframe are directly coupledto the terminals. The chip device also includes a body including awindow defined therein. The body is placed around at least a portion ofthe leadframe and the die such that the metallized back side of the dieis adjacent the window.

[0007] In accordance with one aspect of the present invention, the dieis coupled to the leadframe with solder bumps.

[0008] In accordance with another aspect of the present invention, thechip device includes two dies.

[0009] In accordance with a further aspect of the present invention, amethod of making a chip device includes providing a leadframe includinga plurality of leads and a die attach pad and post, coupling a die tothe die attach pad and post and, encapsulating at least a portion of theleadframe and die such that a metallized back side of the die isadjacent a window defined within the package mold.

[0010] In accordance with another aspect of the present invention, themethod includes configuring leads of the leadframe.

[0011] In accordance with another aspect of the present invention, theconfiguring of the leads includes removing mold flashes and resins fromthe leads, removing dambars, and solder plating the leads.

[0012] In accordance with a further aspect of the present invention, theleadframe is provided with preplated leads.

[0013] In accordance with yet another aspect of the present invention,the leadframe is provided with preplated leads and preformed leads.

[0014] In accordance with a further aspect of the present invention, theleadframe is provided with two die attach pads and posts, wherein afirst die is coupled to a first die attach pad and post, and a seconddie is coupled to a second die attach pad and post.

[0015] In accordance with another aspect of the present invention, thedie is coupled to the leadframe die attach pad and post via solderbumps, wherein the solder bumps are re-flowed.

[0016] Thus, the present invention provides a chip device that includesa thinner package, yet can accommodate a larger die. Indeed, up to a 70%increase in die area over wire bonded parts may be realized.Additionally, the present invention lends itself to packaging multipledies in the same package. The present invention allows a die-to-dieconnection to be achieved using a low resistance path (leadframe based)capable of carrying high current. Furthermore, the present inventionprovides a simplified manufacturing process, especially in theembodiments where preplated and preformed leadframes are provided.

[0017] Other features and advantages of the present invention will beunderstood upon reading and understanding the detailed description ofthe preferred exemplary embodiments, found hereinbelow, in conjunctionwith reference to the drawings, in which like numerals represent likeelements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1A is a top plan view of a chip device in accordance with thepresent invention;

[0019]FIG. 1B is a bottom elevation view of a chip device in accordancewith the present invention;

[0020]FIG. 1C is a sectional view of a chip device in accordance withthe present invention as seen along the line A-A in FIG. 1A;

[0021]FIG. 1D is a side elevation view of a chip device in accordancewith the present invention;

[0022]FIG. 2 is a top plan view of a leadframe for use in making a chipdevice in accordance with the present invention;

[0023]FIG. 3 is a top plan view of an alternative leadframe for use inmaking a chip device in accordance with the present invention;

[0024]FIG. 3A is a top plan view of the leadframe illustrated in FIG. 3a common die attach pad for two dies;

[0025]FIG. 4 is a top plan view of a die for use in making a chip devicein accordance with the present invention;

[0026]FIG. 5 is a bottom plan view of a die coupled to a leadframe andencapsulated with a mold compound;

[0027]FIG. 6 is a top plan view of a old compound encapsulating a diecoupled to a leadframe with dambars removed and marking on the moldcompound;

[0028]FIG. 7A is a top plan view of a preplated and preformed leadframein accordance for making a chip device in accordance with an alternativeembodiment of the present invention; and

[0029]FIG. 7B is a sectional view of the leadframe illustrated in FIG.7A as seen along the line A-A.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS

[0030] A chip device or semiconductor device 10 includes a leadframe 11,a chip or die 12 and a mold compound or body 13. Preferably, backside 14of the die is metallized.

[0031]FIG. 2 illustrates a leadframe 11 a including a plurality of leads20 and a die attach pad 21 a and post 22 a. Preferably, the leadframeconsists of a copper base and is either silver plated or nickel platedon the die attach pad and post. FIG. 3 illustrates a leadframe 11 bsimilar to leadframe 11 a. Leadframe 11 b includes two die attach padsand posts 22 b and thus is used for a chip device that includes twochips or dies. Thus, chip devices with multiple dies may be made. WhileFIG. 3 illustrates two die attach pads, it should be readily apparent tothose skilled in the art that leadframes with more than two die attachpads may be used, and hence, chip devices with more than two dies may bemade.

[0032]FIG. 3A illustrates leadframe 11 c that includes a common dieattach pad 21 c for two dies thus providing a die-to-die connection. Byusing such a leadframe to couple two dies, a low resistance path capableof carrying high current is achieved. For example, in MOSFET devices,this allows bi-directional switches to be fabricated (common sourcecontact).

[0033]FIG. 4 illustrates a die or chip 12. As noted above, back surface14 of the die is preferably back metallized. Preferably, top surface 30of the die is passivated and includes a plurality of solder bumps 31.Most of the solder bumps will serve to connect source region 32 of thechip to leads of the leadframe. Solder bump 33 serves as a gate bump andthus couples gate region 34 of the chip to a gate lead of the leadframevia die attach post 22.

[0034] Once the chip with the array of solder bumps is brought intocontact with the die attach pad and post, the solder is reflowed,preferably with heat, in order to attach the chip to the leadframe andto provide good contact between the chip and the leadframe.

[0035] Once the solder has been reflowed, the chip device isencapsulated with mold compound 13 such that the chip and the die attachpad and post are enveloped by the mold compound.

[0036] As can be seen in FIG. 5, mold compound 13 includes a window 40defined therein. The chip device is encapsulated by the mold compoundsuch that metallized back surface 14 of the die is adjacent to thewindow. Preferably, as can be seen in FIG. 1C, metallized back surface14 is at least partially within window 40 such that back surface 14 issubstantially flush with back surface 41 of mold compound 13. Thus,after encapsulating the chip device with the mold compound, themetallized back surface of the die is exposed through the window. Whenthe chip device is placed on a circuit board for use, this exposed backsurface of the die serves as the drain terminal of the chip device.

[0037] Once mold compound 13 has been added to the chip device, the“package” of the chip device is essentially complete. Dambars 50 areremoved and the leads are cleansed of any mold flashes and resins thatmay have accumulated during the manufacturing process. If desired, topsurface 51 of the mold compound opposite the surface that includes thewindow may be marked with a laser or ink as shown in FIG. 6, forexample, to identify the chip device. The leads are then solder platedand rails 52 at the end of the leads are removed. The leads are thenconfigured by bending or forming them so that the chip may be placed ona circuit board. As can be seen in FIG. 1C, the leads are configured sothat the ends are essentially co-planer with the exposed back surface 14of the die.

[0038] In accordance with an alternative manufacturing process, theleadframe is pre-plated prior to the start of the manufacturing process.Preferably, the leadframe is pre-plated with NiPd. The manufacturingprocess proceeds as described above except the step of solder platingthe leads is no longer required.

[0039] Additionally, in accordance with yet another embodiment of themanufacturing process, the leads of the leadframe are “pre-formed.”Preferably, prior to the manufacturing process, the leadframe is platedwith NiPd and the leads of the leadframe are pre-formed and configured,as can be seen in FIGS. 7A and 7B. Thus, the manufacturing process willproceed as outlined above, but the steps of plating the leads withsolder and configuring the leads is no longer required.

[0040] Accordingly, by providing leadframes for the manufacture of achip device in accordance with the present invention wherein theleadframes are pre-plated and/or the leads are pre-formed, themanufacturing process may be simplified and shortened. This allows for aquicker, more efficient and less expensive manufacturing process to berealized.

[0041] Die 12 may be manufactured in a conventional manner generallyknown in the art for a number of applications.

[0042] Thus, the present invention provides a chip device that includesa thinner package, that can accommodate a larger die by using a singleleadframe and using the back metallized surface of the die as draincontacts. Indeed, up to a 70% increase in die area over wire-bondedparts may be realized. Furthermore, the present invention provides asimplified manufacturing process, especially in the embodiments wherepre-plated and pre-formed leadframes are provided.

[0043] Although the invention has been described with reference tospecific exemplary embodiments, it will be appreciated that it isintended to cover all modifications and equivalents within the scope ofthe appended claims.

What is claimed is:
 1. A chip device comprising: a leadframe including aplurality of leads; a die including a metallized backside and furtherincluding source and gate terminals opposite the metallized backside,the die being coupled to the leadframe such that the leads of theleadframe are directly coupled to the terminals; and a body with awindow defined therein, the body enveloping at least a portion of theleadframe and the die; wherein the die is positioned with respect to thebody such that the metallized backside is adjacent the window.
 2. A chipdevice in accordance with claim 1 wherein the die is coupled to theleadframe with solder bumps.
 3. A chip device in accordance with claim 1wherein the leadframe is silver plated where the leadframe is coupled tothe terminals.
 4. A chip device in accordance with claim 1 wherein theleadframe is nickel plated where the leadframe is coupled to theterminals.
 5. A chip device in accordance with claim 1 wherein thedevice comprises two dies each including a metallized backside and eachfurther including source and gate terminals opposite the metallizedbackside, the dies being coupled to corresponding die attach pads of theleadframe such that the leads of the leadframe are directly coupled tothe terminals, and wherein the body includes two windows defined thereinand the dies are positioned with respect to the body such that themetallized backsides are adjacent a corresponding window.
 6. A chipdevice in accordance with claim 5 wherein the die attach pads arecoupled to one another.
 7. A method of making a chip device, the methodcomprising: providing a leadframe that includes leads; providing a diethat includes a metallized backside; coupling the die to the leadframe;and encapsulating the die with a body such that the metallized backsideof the die is adjacent a window defined within the body.
 8. A method inaccordance with claim 7 further comprising configuring the plurality ofleads.
 9. A method in accordance with claim 8 further comprisingremoving dambars from the leadframe, removing mold flashes and resinsfrom the leads, and solder plating the leads.
 10. A method in accordancewith claim 7 further comprising marking the body on a surface oppositethe window.
 11. A method in accordance with claim 10 wherein the markingis performed with a laser.
 12. A method in accordance with claim 10wherein the marking is performed with ink.
 13. A method in accordancewith claim 7 wherein the leadframe is provided with preplated leads. 14.A method in accordance with claim 7 wherein the leadframe is providedwith preformed leads.
 15. A method in accordance with claim 7 whereinthe leadframe is provided with preplated leads and preformed leads. 16.A method in accordance with claim 7 wherein the die is coupled to theleadframe die attach pad and post via solder bumps, and wherein thesolder bumps are re-flowed.
 17. A method in accordance with claim 7wherein the leadframe is provided with two die attach pads and posts,and the method further comprises providing two dies that each include ametallized back side, and coupling the first of the two dies to a firstdie attach pad and post, coupling a second of the two dies to a seconddie attach pad and post.